Carbon fibers have superior properties such as high mechanical characteristics, chemical resistance, electrical conductivity and thermal conductivity. Therefore, they are widely used in the fields of airplanes, automobiles, leisure goods and the like for the purpose of improving mechanical strength, as well as in the fields of components of electronic equipment and the like for the purpose of imparting electrical conductivity and thermal conductivity.
In order to manufacture the mechanical and functional composite materials described above by use of carbon fibers, it is required that carbon fibers be uniformly dispersed in a solution, a resin solution and a resin. However, since carbon fibers generally have a high cohesive force, they are materials which are hardly uniformly dispersed and so it is desired to provide a method and a dispersant which enable more uniform dispersion.
As a method for uniformly dispersing carbon fibers, carbon nanofibers and the like in an aqueous medium, there are known a method in which a gelatinous dispersion liquid is prepared by adding borax to an aqueous solution of polyvinyl alcohol, and carbon nanofibers are added to this dispersion liquid, followed by stirring (Patent Document 1), and the like.
As a dispersant for uniformly dispersing carbon fibers, carbon nanofibers and the like in an aqueous medium or a non-aqueous medium, the following dispersants are known which are added for improving dispersibility of carbon fibers when carbon fibers are dispersed in an organic solvent solution of an organic solvent-soluble resin: a dispersant for carbon fibers represented by the following general formula (1):
wherein R1, R2, R3 and R4 each independently represent a hydrogen atom, a hydroxyl group, an unsubstituted or substituted C1-30 alkyl group, an unsubstituted or substituted hydroxyalkyl group, an alkyloxy group, an acyloxy group, a carboxyl group, an acyl group, primary to tertiary amino groups, an unsubstituted or substituted aryl group, an unsubstituted or substituted aryloxy group or an unsubstituted or substituted heterocyclic group, R5 and R6 each independently represent a hydrogen atom, an unsubstituted or substituted C1-30 alkyl group, an unsubstituted or substituted aryl group or an unsubstituted or substituted heterocyclic group or R5 and R6 may be combined to form a ring, R7 represents a hydrogen atom, an unsubstituted or substituted C1-30 alkyl group, an unsubstituted or substituted hydroxyalkyl group, an alkyloxy group, an acyloxy group, a carbonyl group, a carboxyl group, primary to tertiary amino groups, an unsubstituted or substituted aryl group, an unsubstituted or substituted aryloxy group or an unsubstituted or substituted heterocyclic group, and X:Y:Z=65 to 90:5 to 30:0 to 10 (Patent Document 2); and a dispersant for carbon fibers represented by the following general formula (1):
wherein R1, R2, R4, R6, R7 and R8 each independently represent a hydrogen atom, a hydroxyl group, an unsubstituted or substituted C1-30 alkyl group, an unsubstituted or substituted hydroxyalkyl group, an alkyloxy group, an acyloxy group, a carboxyl group, an acyl group, primary to tertiary amino groups, an unsubstituted or substituted aryl group, an unsubstituted or substituted aryloxy group or an unsubstituted or substituted heterocyclic group, provided that a hydrogen atom when R6 or R7 is a hydroxyl group may be substituted with an unsubstituted or substituted heterocyclic group, R3, R5 and R9 each independently represent a hydrogen atom, an unsubstituted or substituted C1-30 alkyl group, an unsubstituted or substituted aryl group, an unsubstituted or substituted heterocyclic group, an unsubstituted or substituted pyranosyl group or an unsubstituted or substituted furanosyl group; or when they represent a group bonded via an oxygen atom, they may form a carbonyl group with elimination of its adjacent group, the group bonded to a different carbon may be linked together to form an olefin or a ring, the configuration of a substituent bonded to a chiral carbon may be either axial, equatorial or racemic, and when a glycosidic bond is formed, it may be either α or β; m represents 0 or 1, n represents an integer of from 0 to 2 (Patent Document 3).
Also, the following arts are known: a surfactant having an alkyl ester group, a vinylidene group and an anionic group (Patent Document 4); a dispersant used for carbon fillers which comprises hydroxyalkyl chitosan as a major ingredient (Patent Document 5); a dispersant for carbon material comprising a copolymer (A) which consists of a structural unit (a1) represented by the following formula (1) and a structural unit (a2) represented by the following formula (2):
wherein R1 is a hydrogen atom or a methyl group, R2 is a C16-22 alkyl group, R3 is a hydrogen atom or a methyl group, R4 is a hydrogen atom or a C1-22 alkyl group, AO is a C2-4 oxyalkylene group, n is an integer of 1 to 100,wherein the copolymer (A) has a mass ratio of (a1) to (a2), i.e., (a1)/(a2) of 90/10 to 10/90, and a weight-average molecular weight of 3,000 to 500,000 (Patent Document 6); and an aqueous dispersant which is a polyether-based compound represented by the following formula (1):
wherein A1O is an oxyethylene group, a is 3 to 25, A2O is an oxypropylene group, b is 1 to 10, the conditions of 5≤a+b≤30 and 1≤a/b≤5 are satisfied, R is a hydrogen atom or a C1-4 hydrocarbon group, n is 1 to 4, and having a molecular weight of 1000 to 5000 (Patent Document 7).